Conventionally, a variety of standards have been proposed for an interface between information devices. For example, HDMI (High-Definition Multimedia Interface) is known as a high-speed serial interface. Devices which adopt the HDMI as an interface are disclosed in Japanese Patent Application Laid-Open No. 2005-189587 and Japanese Patent Application Laid-Open No. 2004-248080. The HDMI is well known as a digital interface which transmits high-quality audio/video (A/V) content data between a source device such as a DVD (Digital Versatile Disk) device, an STB (Set-Top Box) and the like and a sink device such as a plasma display device, a digital television set and the like. The HDMI is characterized by the capability of transmitting encrypted information, the capability of transmitting a video signal and an audio signal at the same time, the capability of transmitting uncompressed data in real time, a transmission rate of 3.5 Gbps and a wide transmission band, and the like.
In the conventional information device, an interface circuit for interfacing with the outside based on the HDMI or other standards and a main processing circuit for performing signal processing related to a main function in the information device have been controlled by the same microcomputer. In a display device such as a plasma display device as an example, a receiver circuit for receiving and outputting a video signal, an audio signal and the like transmitted from a source device such as a DVD device by using a predetermined interface and a signal processing circuit for performing a format conversion process and like related to video display and audio output upon the video and audio signals outputted from the receiver circuit are controlled by the same microcomputer. Thus, the single microcomputer is required to execute firmware for controlling the interface circuit and firmware for controlling the main processing circuit, and therefore has the problem of bearing a heavy load during real-time processing. It is also necessary to develop the firmware for controlling the interface circuit and the firmware for controlling the main processing circuit in the same environment. This provides an increased development load, and becomes one of the causes of the slowdown of the development. Similar problems arise in the source device such as the DVD device.